Prevention of paraffin deposition and plugging



2,817,635 Patented Dec. 24, 1957 PREVENTIUN @F PARAFFHN DEPOSITION ANDPLUGGING No Drawing. Application duly 27, 1954 Serial No. 446,156

19 Claims. (Cl. 2523.55)

Nathan, New

This invention relates to the transportation of fluids containing Waxymaterials which tend to deposit therefrom and form a coating on thesurfaces in contact with these fluids and waxy materials. Moreparticularly, this invention relates to the transportation ofwax-containing fluids such as petroleum or crude oil through productionconduits, gathering and collecting lines, and the like. Still morespecifically, this invention relates to compositions and a method forthe prevention of wax plugging or clogging in production ortransportation conduits.

In one of its embodiments this invention is concerned with those oilwells which tend to lay down or deposit objectionable paraflinicdeposits upon the interior surfaces of the production and/or gatheringpipe system. Often in the production of Waxy crudes the composition ofthe produced waxy crude is such that the decrease in temperature and/ orpressure which the produced waxy crude oil usually undergoes duringproduction, i. e., upon being elevated through the production tubing orbeing transported within the gathering system, results in the separationof adherent waxy solids from the produced liquid oil. Frequently in suchproduction and gathering systems cooling occurs through the conduitwalls with the result that the separated or precipitated wax tends tostick or deposit upon the inside walls of the conduits handling theproduced oil. It has been noted that the wax which separates has atendency to stick to metal surfaces in contact with the same,particularly ferruginous surfaces such as those of iron or steel pipes,with the result that a layer of waxy materials is deposited thereon.Uusually this waxy deposit layer builds up, progressively increasing inthickness, and in the case of conduits this deposited waxy layerincreasingly constricts the flow passage with the result that the fiowof fluid therethrough is severely restricted and in some instanceseventually completely shut oil. Removal of such waxy deposits isdifflcult and costly.

It is an obpect of this invention to provide a composition and methodfor inhibiting the tendency of waxy materials to deposit and to stickupon surfaces in contact with the same.

It is another object of this invention to provide a composition andmethod useful for preventing the formation of wax plugs in productionconduits or systems handling a Waxy crude oil.

It is another object of this invention to provide an improved method forthe prevention of wax deposition and plugging within ferruginous pipeshandling a waxy crude.

These and other objects of this invention and how they are accomplishedwill become more apparent in the light of the accompanying disclosure.

In accordance with this invention wax deposition upon surfaces incontact with waxy materials which exhibit a tendency to stick theretoand to deposit thereon a layer of Waxy material is inhibited and/orsubstantially pre vented by the presence of an alkali metal silicate andan organic non-ionic, surface-active agent. Suitable alkali metalsilicates include sodium silicate, potassium silicate,

or mixtures thereof, particularly aqueous solutions thereof. Suitableorganic non-ionic, surface-active agents include those solid or liquidpolyoxyalkylene derivatives of hexitol anhydride partial long chainfatty acid esters. These particular materials are represented by thepolyoxyethylene derivatives of sorbitan monolaurate, sorbitanmonopalmitate, sorbitan 'rnonostearate, sorbitan tristearate andsorbitan oleate. A particularly effective non-ionic, surface-activeagent in combination with aqueous sodium silicate is a polyoxyethylenederivative of sorbitan trioleate. In general, the above-identifiednon-ionic surface active agents are oily liquids, in some instances waxysolids, and exhibit a specific gravity 'in the range LOO-1.3. Theseabove-identified surface-active agents are manufactured by The AtlasPowder Company and are sold under the trade name Tween, e' g. Tween No.20, 21, 40, 60, 61, 65, 80, 81 and 85. For example, Tween 85 identifiesa polyoxyethylene derivative of sorbitan trioleate and Tween 81identifies a polyoxyethylene derivative of sorbitan monooleate. For themost part these materials are soluble in a hydrocarbon fluid such astoluene and in a polar organic solvents such as ethyl alcohol.

In the practice of this invention there is injected into a conduitcontaining a fluid, such as a crude oil, from which waxy materials tendto separate with the resultant formation of a waxy layer or deposit uponthe surfaces of the conduit in contact therewith, amounts of an alkalimetal silicate and an organic non-ionic surface-active agent such as apolyoxyethylene derivative of a hexitol anhydride partial long chainfatty acid ester sufiicient to inhibit wax deposition. In a particularapplication of this invention for the prevention or inhibition of waxdeposition on the surfaces of a production string in an oil wellproducing a waxy crude, there is injected into the well casing thematerials in accordance with this invention. Eventually from the casingthe particular combination "of materials of this invention will flowwith the produced waxy crude into the production string so as tointermingle and be produced with the waxy crude thereby preventing waxdeposition within the production tubing.

In the practice of this invention it is preferred to continuously addthe alkali metal silicate and the organic non-ionic surface-active agentto the waxy fluids from which wax deposition occurs. The particularcombination of materials of this invention may be added separately or inadmixture. Usually an amount of each of theadded materials in the range0.001-1 percent by Weight, preferably in the range 0.01-0.5 percentbased on the fluid from which wax deposition occurs, is satisfactory.More or less of each of the above components may be added if desired. Itis preferred however in the practice of this invention to employsubstantially equal amounts by weight of the alkali metal silicate andthe organic non-ionic surface-active agent.

The following is explanatory of the practice of this invention and theadvantages to be derived therefrom. One percent by weight of a highmelting point paraffin wax derived from Dayton Crude, which wax wasfound to separate from the Dayton Crude in the field and cause severeline plugging, was added toDayton Crude. It had been found in actualtests that the addition of lpercent of this high melting point paraflinWax to the Dayton Crude produced a waxy fluid which would depositparaffin therefrom and yield reproducible results.

The resulting waxy fluid containing the 1 percent high melting pointparaffin wax was heated to 45 C. and pumped at a rate of about 1000 cc.per minute through a Mr inch 1. D. steel tubing 9 feet long. A S-footsection of this tubing was immersed in a water bath maintained at atemperature in the range 30-32" C.' That section of the tubing immersedin the water was in the form of an elongated coil, the turns in the coilbeing made by 90- degree elbows. The pressure on the pump circulatingthe waxy fluid through the tubing was measured by means of a mercurymanometer having a maximum capacity of 10.0 cm. of mercury. During thetests the relative effectiveness of the additives tested was determinedby measuriug the time required for the tubing to plug with depositedwax, plugging being considered complete when the pressure on the pumpdischarge exceeded the capacity of the manometer. During the tests thealkali metal silicate employed was added as a 2 percent water solutionof sodium silicate. The waxy fluids undergoing tests were prepared byadding thereto 500 cc. of 2 percent sodium silicate solution and/or 10cc. of the particular polyoxyalkylene derivative of a hexitol anhydridepartial long chain fatty acid ester being tested. The resulting testfluids were stirred vigorously while being heated to 45 C., stirringbeing continued throughout the duration of the experiment in order toinsure adequate mixing of the silicate solution, the crude oil and theorganic non-ionic surface-active agent.

The results of the foregoing described experiments may be summarized asfollows:

A. Repeated runs on the Dayton Crude alone plus added high melting pointparaffin wax produced plugging in about 34 hours.

B. When 500 cc. of water alone were added to the waxy Dayton Crude thetime required for plugging was increased to about 5 /2 hours but thesystem showed no tendency to purge itself when the pressure began toincrease.

C. With 500 cc. of water plus cc. of Tween 85 (a polyoxyethylenederivative of sorbitan trioleate having a specific gravity in the rangel.00l.05 and exhibiting solubility in toluene and ethyl alcohol), addedto the waxy Dayton Crude the plugging time was about the same asmentioned in A, but there was a tendency for the system to purge itselfof any deposited paratfin wax as the pressure within the systemincreased. Accordingly, this combination of water and Tween 85 impartedself-purging properties to the system undergoing tests.

D. The addition of sodium silicate alone (500 cc. of 2 percent aqueoussolution) to the waxy Dayton Crude merely increased the time requiredfor plugging but no self-purging action was indicated by the system.

E. The addition of 500 cc. of a 2 percent aqueous sodium silicatesolution and 10 cc. of Tween 85 to 7 liters of the waxy Dayton Crudecompletely eliminated plugging. It was noticed that the nature of thedeposited wax was changed from a hard crystalline waxy material, such aswas deposited in the tests described in A, to an amorphous waxymaterial. Each time the pressure in the system increased the depositedwaxy materials would slough off the wall of the tubing and be carriedout of the system. The above-described test was carried out for morethan 21 hours duration without plugging the system.

In view of the above tests it is apparent that the combination of thematerials of this invention not only inhibit wax deposition out alsoimpart to the system in which they are present self-purging orself-cleaning properties such that eventually any deposited waxymaterials slough off and are carried along in the fluid stream.

As will be apparent to those skilled in the art in the light of thisdisclosure, many modifications, alterations and changes are possiblewithout departing from the spirit and scope of this invention.

We claim:

1. In the transportation of a fluid through a conduit, wherein saidfluid contains waxy materials which tend to deposit and build upobectionable deposits of said waxy materials on the surface of saidconduit in contact with said fluid, the improvement which comprisesinjecting into said fluid being transported through said conduitsubstantially equal amounts of an alkali metal silicate and a non-ionic,surface-activepolyoxyalkylene derivative of a 4 hexitol 'anhydridepartial long chain fatty acid ester, said amounts being suflicient toprevent a build-up of objectionable deposits of said waxy materials onthe surface of said conduit.

2. A method in accordance with claim 1 wherein said alkali metalsilicate is sodium silicate.

3. The method in accordance with claim 1 wherein said alkali metalsilicate is sodium silicate in the form of an aqueous solution thereof.

4. The method in accordance with claim 1 wherein said non-ionicsurface-active derivative is a polyoxyalkylene derivative of sorbitantrioleate.

5. The method in accordance with claim 1 wherein said non-ionicsurface-active derivative is a polyoxyethylene derivative of sorbitantrioleate.

6. The method in accordance with claim 1 wherein equal amounts of saidalkali metal silicate and said nonionic surface-active derivative areinjected into said fluid.

7. The method in accordance with claim 1 wherein said surface of saidconduit is a ferruginous.

8. The method in accordance with claim 1 wherein said fluid is ahydrocarbon fluid such as a waxy crude oil.

9. The method in accordance with claim 1 wherein said alkali metalsilicate and said non-ionic surface-active derivative are each injectedinto said fluid in an amount in the range 0.001-1 percent by weightbased on said fluid.

10. The method in accordance with claim 1 wherein said alkali metalsilicate is sodium silicate and wherein said non-ionic surface-activederivative is a polyoxyethylene derivative of a hexitol anhydridepartial long chain f tty acid ester, said sodium silicate and saidpolyoxyethylene derivative being injected in equal amounts by weight.

11. The method in accordance with claim 10 wherein each of said amountsof sodium silicate and said polyoxyethylene derivative is in the range0.001-1 percent by weight based on said fluid.

12. The method in accordance with claim 1 wherein said non-ionicsurface-active derivative is a polyoxyalkylene derivative of sorbitanmonooleate.

13. The method in accordance with claim 1 wherein said n0n-ionicsurface-active derivative is a polyoxyalkylene derivative of sorbitanmonostearate.

14. The method in accordance with claim 1 wherein said non-ionicsurface-active derivative is a polyoxyalkylene derivative of sorbitanmonopalmitate.

15. A composition of matter suitable for injection into a fluid whichcontains waxy materials which tend to build up objectionable deposits ofsaid waxy materials upon surfaces in contact therewith whereby theformation of said waxy deposits is inhibited, comprising an alkali metalsilicate and a non-ionic surface-active polyoxyalkylene derivative of ahexitol anhydride partial long chain fatty acid ester, the weight ratioof said alkali metal silicate to said polyoxyalkylene derivative beingabout 1:1.

16. A composition in accordance with claim 15 containing equal amountsby weight of sodium silicate and a non-ionic surface-activepolyoxyethylene derivative of a hexitol anhydride partial longchainfatty acid ester.

17. A composition in accordance with claim 16 wherein said derivative isa polyoxyethylene derivative of sorbitan trioleate.

18. A composition of matter suitable for injection into a hydrocarbonfluid which tends to deposit a layer of waxy materials upon ferruginoussurface in contact with said fluid whereby the deposition of said waxymaterials is inhibited, consisting essentially of substantially equalamounts by weight of a polyoxyethylene derivative of a hexitol anhydridepartial long chain fatty acid ester and an alkali metal silicate.

19. A composition in accordance with claim 18 Wherein saidpolyoxycthyiene derivative is a polyoxyethylene derivative of sorbitantrioleate and wherein said alkali metal silicate sodium silicate.

(References on following page) 5 References Cited in the file of thispatent OTHER REFERENCES UNITED STATES PATENTS PQ Sih'cates of Soda,pamphlet pub. by Philadelphia Quartz 00., page 6. 522%??? C 1 ari; :tal:i 32 :3; 1333 5 Atlas Spam and Tweens, pamphlet June 1945, by

2,753,303 Barker July 3, 1956 Atlas Powder 0)., of Wilmington, Delaware,page 17.

1. IN THE TRANSPORTATION OF A FLUID THROUGH A CONDUIT, WHEREIN SAIDFLUID CONTAINS WAXY MATERIALS WHICH TEND TO DEPOSIT AND BUILD UPOBECTIONABLE DEPOSITS OF SAID WAXY MATERIALS ON THE SURFACE OF SAIDCONDUIT IN CONTACT WITH SAID FLUID, THE IMPROVEMENT WHICH COMPRISESINJECTING INTO SAID FLUID BEING TRANSPORTED THROUGH SAID CONDUITSUBSTANTIALLY EQUAL AMOUNTS OF AN ALKALI METAL SILICATE AND A NON-IONIC,SURFACE-ACTIVE POLYOXYALKYLENE DERIVATION OF A HEXITOL ANHYDRIDE PARTIALLONG CHAIN FATTY ACID ESTER, SAID AMOUNTS BEING SUFFICIENT TO PREVENT ABUILD-UP OF OBJECTIONABLE DEPOSITS OF SAID WAXY MATERIALS ON THE SURFACEOF SAID CONDUIT.